Scott Hanselman

How to use Windows 10's built-in OpenSSH to automatically SSH into a remote Linux machine

January 23, '19 Comments [6] Posted in DotNetCore | Hardware | Open Source
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In working on getting Remote debugging with VS Code on Windows to a Raspberry Pi using .NET Core on ARM in my last post, I was looking for optimizations and realized that I was using plink/putty for my SSH tunnel. Putty is one of those tools that we (as developers) often take for granted, but ideally I could do stuff like this without installing yet another tool. Being able to use out of the box tools has a lot of value.

A friend pointed out this part where I'm using plink.exe to ssh into the remote Linux machine to launch the VS Debugger:

"pipeTransport": {
"pipeCwd": "${workspaceFolder}",
"pipeProgram": "${env:ChocolateyInstall}\\bin\\PLINK.EXE",
"pipeArgs": [
"-pw",
"raspberry",
"root@crowpi.lan"
],
"debuggerPath": "/home/pi/vsdbg/vsdbg"
}

I could use Linux/bash that's built into Windows 10 for years now. As you may know, Windows 10 can run many Linuxes out of the box. If I have a Linux distro configured, I can call Linux commands locally from CMD or PowerShell. For example, here you see I have three Linuxes and one is the default. I can call "wsl" and any command line is passed in.

C:\Users\scott> wslconfig /l
Windows Subsystem for Linux Distributions:
Ubuntu-18.04 (Default)
WLinux
Debian
C:\Users\scott> wsl ls ~/
forablog forablog.2 forablog.2.save forablog.pub myopenaps notreal notreal.pub test.txt

So theoretically I could "wsl ssh" and use that Linux's ssh, but again, requires setup and it's a little silly. Windows 10 now supports OpenSSL already!

Open an admin PowerShell to see if you have it installed. Here I have the client software installed but not the server.

PS> Get-WindowsCapability -Online | ? Name -like 'OpenSSH*'

Name : OpenSSH.Client~~~~0.0.1.0
State : Installed

Name : OpenSSH.Server~~~~0.0.1.0
State : NotPresent

You can then add the client (or server) with this one-time command:

Add-WindowsCapability -Online -Name OpenSSH.Client~~~~0.0.1.0

You'll get all the standard OpenSSH stuff that one would want.

OpenSSL tools on Windows

Let's say now that I want to be able to ssh (shoosh!) into a remote Linux machine using PGP keys rather than with a password. It's much more convenient and secure. I'll be ssh'ing with my Windows SSH into a remote Linux machine. You can see where ssh is installed:

C:\Users\scott>where ssh
C:\Windows\System32\OpenSSH\ssh.exe

Level set - What are we doing and what are we trying to accomplish?

I want to be able to type "ssh pi@crowpi" from my Windows machine and automatically be logged in.

I will

  • Make a key on my Window machine. The FROM. I want to ssh FROM here TO the Linux machine.
  • Tell the Linux machine (by transferring it over) about the public piece of my key and add it to a specific user's allowed_keys.
  • PROFIT

Here's what I did. Note you can do this is several ways. You can gen the key on the Linux side and scp it over, you can use a custom key and give it a filename, you can use a password as you like. Just get the essence right.

Below, note that when the command line is C:\ I'm on Windows and when it's $ I'm on the remote Linux machine/Raspberry Pi.

  • gen the key on Windows with ssh-keygen
  • I ssh'ed over to Linux and note I'm prompted for a password, as expected.
  • I "ls" to see that I have a .ssh/ folder. Cool. You can see authorized_keys is in there, you may or may no have this file or folder. Make the ~/.ssh folder if you don't.
  • Exit out. I'm in Windows now.
  • Look closely here. I'm "scott" on Windows so my public key is in c:\users\scott\.ssh\id_rsa.pub. Yours could be in a file you named earlier, be conscious.
    • I'm type'ing (cat on Linux is type on Windows) that text file out and piping it into SSH where I login that remote machine with the user pi and I then cat (on the Linux side now) and append >> that text to the .ssh/authorized_keys folder. The ~ folder is implied but could be added if you like.
  • Now when I ssh pi@crowpi I should NOT be prompted for a password.

Here's the whole thing.

C:\Users\scott\Desktop> ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (C:\Users\scott/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in C:\Users\scott/.ssh/id_rsa.
Your public key has been saved in C:\Users\scott/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:x2vJHHXwosSSzLHQWziyx4II+scott@IRONHEART
The key's randomart image is:
+---[RSA 2048]----+
| . .... . |
|..+. .=+=. o |
| .. |
+----[SHA256]-----+
C:\Users\scott\Desktop> ssh pi@crowpi
pi@crowpi's password:
Linux crowpi 2018 armv7l

pi@crowpi:~ $ ls .ssh/
authorized_keys id_rsa id_rsa.pub known_hosts
pi@crowpi:~ $ exit
logout
Connection to crowpi closed.
C:\Users\scott\Desktop> type C:\Users\scott\.ssh\id_rsa.pub | ssh pi@crowpi 'cat >> .ssh/authorized_keys'
pi@crowpi's password:
C:\Users\scott\Desktop> ssh pi@crowpi
pi@crowpi: ~ $

Fab. At this point I could go BACK to my Windows' Visual Studio Code launch.json and simplify it to NOT use Plink/Putty and just use ssh and the ssh key management that's included with Windows.

"pipeTransport": {
"pipeCwd": "${workspaceFolder}",
"pipeProgram": "ssh",
"pipeArgs": [
"pi@crowpi.lan"
],
"debuggerPath": "/home/pi/vsdbg/vsdbg"
}

Cool!

NOTE: In my previous blog post some folks noted I am logging in as "root." That's an artifact of the way that .NET Core is accessing the GPIO pins. That won't be like that forever.

Thoughts? I hope this helps someone.


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Remote debugging with VS Code on Windows to a Raspberry Pi using .NET Core on ARM

January 18, '19 Comments [8] Posted in DotNetCore | Hardware | Open Source
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I've been playing with my new "CrowPi" from Elecrow. It's a great Raspberrry Pi STEM kit that is entirely self-contained in a small case. It includes a touch screen and a TON of sensors, LCDs, matrix display, sensors, buzzers, breadboard, etc.

NOTE: I talked to the #CrowPi people and they gave me an Amazon COUPON that's ~$70 off! The coupon is 8EMCVI56 and will work until Jan 31, add it during checkout. The Advanced Kit is at https://amzn.to/2SVtXl2 #ref and includes everything, touchscreen, keyboard, mouse, power, SNES controllers, motors, etc. I will be doing a full review soon. Short review is, it's amazing.

I was checking out daily builds of the new open source .NET Core System.Device.Gpio that lets me use C# to talk to the General Purpose Input/Output pins (GPIO) on the Raspberry Pi. However, my "developer's inner loop" was somewhat manual. The developer's inner loop is that "write code, run code, change code" loop that we all do. If you find yourself typing repetitive commands that deploy or test your code but don't write new code, you'll want to try to optimize that inner loop and get it down to one keystroke (or zero in the case of automatic test).

Rasbperry Pi Debugging with VS CodeIn my example, I was writing my code in Visual Studio Code on my Windows machine, building the code locally, then running a "publish.bat" that would scp (secure copy) the resulting binaries over to the Raspberry Pi. Then in another command prompt that was ssh'ed into the Pi, I would chmod the resulting binary and run it. This was tedious and annoying, however as programmers sometimes we stop noticing it and just put up with the repetitive motion.

A good (kind of a joke, but not really) programmer rule of thumb is - if you do something twice, automate it.

I wanted to be able not only to make the deployment automatic, but also ideally I'd be able to interactively debug my C#/.NET Core code remotely. That means I'm writing C# in Visual Studio Code on my Windows machine, I hit "F5" to start a debug session and my app is compiled, published, run, and I attached to a remote debugger running on the Raspberry Pi, AND I'm dropped into a debugging session with a breakpoint set. All with one keystroke. This is common practice with local apps, but for remote apps - and ones that span two CPU architectures - it can take a smidge of setup.

Starting with instructions here: https://github.com/OmniSharp/omnisharp-vscode/wiki/Attaching-to-remote-processes and here: https://github.com/OmniSharp/omnisharp-vscode/wiki/Remote-Debugging-On-Linux-Arm and a little help from Jose Perez Rodriguez at work, here's what I came up with.

Setting up Remote Debugging from Visual Code on Windows to a Raspberry Pi running C# and .NET Core

First, I'm assuming you've got .NET Core on both your Windows machine and Raspberry Pi. You've also installed Visual Studio Code on you Windows machine and you've installed the C# extension.

On the Raspberry Pi

I'm ssh'ing into my Pi from Windows 10. Windows 10 includes ssh out of the box now, but you can also ssh from WSL (Windows Subsystem for Linux).

  1. Install the VS remote debugger on your Pi by running this command:
    curl -sSL https://aka.ms/getvsdbgsh | /bin/sh /dev/stdin -v latest -l ~/vsdbg
  2. ​To debug you will need to run the program as root, so we'll need to be able to remote launch the program as root as well. For this, we need to first set a password for the root user in your pi, which you can do by running:
    sudo passwd root
  3. Then we need to enable ssh connections using root, by running :
    sudo nano /etc/ssh/sshd_config        
    and adding a line that reads:
    PermitRootLogin yes
  4. reboot the pi: sudo reboot

VSDbg looks like this getting installed:

pi@crowpi:~/Desktop/rpitest$ curl -sSL https://aka.ms/getvsdbgsh | /bin/sh /dev/stdin -v latest -l ~/vsdbg
Info: Creating install directory
Using arguments
Version : 'latest'
Location : '/home/pi/vsdbg'
SkipDownloads : 'false'
LaunchVsDbgAfter : 'false'
RemoveExistingOnUpgrade : 'false'
Info: Using vsdbg version '16.0.11220.2'
Info: Previous installation at '/home/pi/vsdbg' not found
Info: Using Runtime ID 'linux-arm'
Downloading https://vsdebugger.azureedge.net/vsdbg-16-0-11220-2/vsdbg-linux-arm.zip
Info: Successfully installed vsdbg at '/home/pi/vsdbg'

At this point I've got vsdbg installed. You can go read about the MI Debug Engine here. "The Visual Studio MI Debug Engine ("MIEngine") provides an open-source Visual Studio Debugger extension that works with MI-enabled debuggers such as gdb, lldb, and clrdbg."

On the Windows Machine

Note that there are a half dozen ways to do this. Since I had a publish.bat already that looked like this, after installing putty with "choco install putty" on my Windows machine. I'm a big fan of pushd and popd and I'll tell you this, they aren't used or known enough.

dotnet publish -r linux-arm /p:ShowLinkerSizeComparison=true 
pushd .\bin\Debug\netcoreapp2.1\linux-arm\publish
pscp -pw raspberry -v -r .\* pi@crowpi.lan:/home/pi/Desktop/rpitest
popd

On Windows, I want to add two things to my .vscode folder. I'll need a launch.json that has my "Launch target" and I'll need some tasks in my tasks.json to support that. I added the "publish" task myself. My publish task calls out to publish.bat. It could also do the stuff above if I wanted. Note that I made publish "dependsOn" build, and I removed/cleared problemMatcher. If you wanted, you could write a regEx that would detect if the publish failed.

{
"version": "2.0.0",
"tasks": [
{
"label": "build",
"command": "dotnet",
"type": "process",
"args": [
"build",
"${workspaceFolder}/rpitest.csproj"
],
"problemMatcher": "$msCompile"
},
{
"label": "publish",
"type": "shell",
"dependsOn": "build",
"presentation": {
"reveal": "always",
"panel": "new"
},
"options": {
"cwd": "${workspaceFolder}"
},
"windows": {
"command": "${cwd}\\publish.bat"
},
"problemMatcher": []
}
]
}

Then in my launch.json, I have this to launch the remote console. This can be a little confusing because it's mixing paths that are local to Windows with paths that are local to the Raspberry Pi. For example, pipeProgram is using the Chocolatey installation of Putty's Plink. But program and args and cwd are all remote (or local to) the Raspberry Pi.

"configurations": [
{
"name": ".NET Core Launch (remote console)",
"type": "coreclr",
"request": "launch",
"preLaunchTask": "build",
"program": "/home/pi/dotnet/dotnet",
"args": ["/home/pi/Desktop/rpitest/rpitest.dll"],
"cwd": "/home/pi/Desktop/rpitest",
"stopAtEntry": false,
"console": "internalConsole",
"pipeTransport": {
"pipeCwd": "${workspaceFolder}",
"pipeProgram": "${env:ChocolateyInstall}\\bin\\PLINK.EXE",
"pipeArgs": [
"-pw",
"raspberry",
"root@crowpi.lan"
],
"debuggerPath": "/home/pi/vsdbg/vsdbg"
}
}

Note the debugger path lines up with the location above that we installed vsdbg.

Remote debugging with VS Code on Windows to a Raspberry Pi using .NET Core

It's worth pointing out that while I'm doing this for C# it's not C# specific. You could setup remote debugging with VS Code using these building blocks with any environment.

The result here is that my developer's inner loop is now just pressing F5! What improvements would YOU make?


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Installing the .NET Core 2.x SDK on a Raspberry Pi and Blinking an LED with System.Device.Gpio

January 16, '19 Comments [10] Posted in DotNetCore | Hardware | Open Source
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The CrowPi from Elecrow is an amazing STEM KitI've written about running .NET Core on Raspberry Pis before, although support was initially limited. Now that Linux ARM32 is a supported distro, what else can we do?

We can certainly quickly and easily install Docker on a Raspberry Pi and be running C# and .NET Core programs in minutes. We can run .NET Core in a stack of Raspberry Pis as a Kubernetes Cluster, making our own tiny cloud and install a serverless platform in it like OpenFaas!

If you have a Raspberry Pi 3 with Raspbian on it like I do, check out https://dotnet.microsoft.com/download/dotnet-core/2.2 and note that last part of the URL. You can ask for /2.1, /2.0, etc, just in case you're reading this post in the future, like tomorrow. ;) Everything is always at https://dotnet.microsoft.com/download/archives so you can tell what's Current and what's not.

For example, if I end up here https://dotnet.microsoft.com/download/thank-you/dotnet-sdk-2.2.102-linux-arm32-binaries I can grab the exact blob URL from the "try again" link and then wget it on my Raspberry Pi. You'll want to get a few prerequisites first. Note these blob links change when new stuff comes out, so you'll want to double check to get latest.

sudo apt-get install curl libunwind8 gettext
wget https://download.visualstudio.microsoft.com/download/pr/9650e3a6-0399-4330-a363-1add761127f9/14d80726c16d0e3d36db2ee5c11928e4/dotnet-sdk-2.2.102-linux-arm.tar.gz
wget https://download.visualstudio.microsoft.com/download/pr/9d049226-1f28-4d3d-a4ff-314e56b223c5/f67ab05a3d70b2bff46ff25e2b3acd2a/aspnetcore-runtime-2.2.1-linux-arm.tar.gz

I got the Linux ARM 32-bit SDK as well as the ASP.NET Runtime so I have those packages available for any web apps I choose to make.

Then we'll extract. You can set it up as a user off of $HOME or in /opt/dotnet and then link to /usr/local/bin.

mkdir -p $HOME/dotnet && tar zxf dotnet-sdk-2.2.102-linux-arm.tar.gz -C $HOME/dotnet
export DOTNET_ROOT=$HOME/dotnet
export PATH=$PATH:$HOME/dotnet

Don't forget to untar the ASP.NET Runtime as well.

tar zxf aspnetcore-runtime-2.2.1-linux-arm.tar.gz -C $HOME/dotnet

Cool. You will want to add the PATH to your profile if you want it to survive restarts. Then run "dotnet --info" to see if it works.

pi@crowpi:~ $ dotnet --info
.NET Core SDK (reflecting any global.json):
Version: 2.2.102

Runtime Environment:
OS Name: raspbian
OS Version: 9
OS Platform: Linux
RID: linux-arm
Base Path: /home/pi/dotnet/sdk/2.2.102/

Host (useful for support):
Version: 2.2.1

.NET Core SDKs installed:
2.2.102 [/home/pi/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.2.1 [/home/pi/dotnet/shared/Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.2.1 [/home/pi/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.2.1 [/home/pi/dotnet/shared/Microsoft.NETCore.App]

Looks good.

At this point I have BOTH the .NET Core runtime (for running stuff) as well as all the ASP.NET runtime for web apps or little microservices AND the .NET SDK which means I can actually compile code (slowly) on the Pi itself. It's up to me/you. If you aren't ever going to develop (compile code) on the Raspberry Pi, you can just install the runtime, but I think it's nice to be prepared.

I am installing all this on a wonderful Raspberry Pi kit called a "CrowPi." They had a successful KickStarter and are now selling a Raspberry Pi Educational Kit with an attached custom board with dozens of components. Rather than having to connect motion sensors, sound sensors, touch sensors, switches, buttons, and carry around a bunch of wires, you can experiment and play with stuff in a very organized case that also has a 7inch HDMI touch screen. They also have 21 great Python Video Courses on their YouTube Channel on how to get started with hardware. It's a joy of a device. More on that later.

NOTE: I talked to the #CrowPi people and they gave me an Amazon COUPON that's ~$70 off! The coupon is 8EMCVI56 and will work until Jan 31, add it during checkout. The Advanced Kit is at https://amzn.to/2SVtXl2 #ref and includes everything, touchscreen, keyboard, mouse, power, SNES controllers, motors, etc. I will be doing a full review soon. Short review is, it's amazing.

Now that .NET Core is installed, I can start exploring the fun happening over at https://github.com/dotnet/iot. It's filled with lots of new functionality inside of System.Device.Gpio. Remember that GPIO means "General Purpose Input/Output" which, on a Raspberry Pi, is connected to a ribbon cable on the CrowPi with lots of cool sensors ready to go!

I could build my Raspberry Pi apps on my Windows/Mac/Linux machine and I'll find it much faster to compile. Then I can "scp" (secure copy) it over to the Pi. It's nice to point out that Windows 10 includes scp.exe now by default!

In this example, by adding -r linux-arm I'm copying a complete self-contained app over the Pi, so don't actually need to install .NET Core like I did above. If instead, I didn't use -r (to declare a specific runtime) then I would need to make sure I've got the right versions on my dev box vs my RPi, so consider what's best for you.

Here I am in my Windows machine that also has the same version of the .NET Core SDK installed. I'm in .\rpitest with a console app I made with "dotnet new console." Now I want to build and copy it over to the Pi.

dotnet publish -r linux-arm
cd bin\Debug\netcore2.1\linux-arm\publish
scp -r . pi@crowpi:/home/pi/Desktop/rpitest

From the Pi, I'll need to "sudo chmod +x" the rpitest application to make sure it is executable.

There's a brilliant video from Cam Soper that shows you in great detail how to run .NET Core 2.x on a Raspberry Pi and I recommend you check it out as well.

IoT devices expose much more than serial ports. They typically expose multiple kinds of pins that can be programmatically used to read sensors, drive LED/LCD/eInk displays and communicate with our devices. .NET Core now has APIs for GPIO, PWM, SPI, and I²C pin types.

These APIs are available via the System.Device.GPIO NuGet package. It will be supported for .NET Core 2.1 and later releases. There's some basic samples here https://github.com/dotnet/iot/blob/master/samples/README.md to start with.

From Microsoft:

Most of our effort has been spent on supporting these APIs in Raspberry Pi 3. We plan to support other devices, like the Hummingboard. Please tell us which boards are important to you. We are in the process of testing Mono on the Raspberry Pi Zero.

For now System.Device.Gpio is a prelease so you'll want to add a nuget.config to your project with the path to the dailies:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
<packageSources>
<clear />
<add key="myget.org" value="https://dotnet.myget.org/F/dotnet-core/api/v3/index.json" />
<add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
</packageSources>
</configuration>

Add a reference to System.Device.Gpio or (at the time of this writing) version 0.1.0-prerelease.19065.1. Now let's do something!

Here I'm just blinking this LED!

Console.WriteLine("Hello World!");
GpioController controller = new GpioController(PinNumberingScheme.Board);
var pin = 37;
var lightTime = 300;

controller.OpenPin(pin, PinMode.Output);
try {
while (true) {
controller.Write(pin, PinValue.High);
Thread.Sleep(lightTime);
controller.Write(pin, PinValue.Low);
Thread.Sleep(lightTime);
}
}
finally {
controller.ClosePin(pin);
}

Yay! Step zero works! Every cool IoT projects starts with a blinking LED!

Blinking LEDs ZOMG

Do be aware that System.Device.Gpio is moving VERY fast and some of this code and the samples may not work if namespaces or class names change. It'll settle down soon.

Great stuff though! Go get involved over at https://github.com/dotnet/iot as they are actively working on drivers/abstractions for Windows, Linux, etc and you could even submit a PR for a device like an LCD or simple sensor! I've only been playing for an hour but I will report back as I try new experiments with my kids.


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Using Visual Studio Code to program Circuit Python with an AdaFruit NeoTrellis M4

December 26, '18 Comments [3] Posted in Hardware | Open Source | Python
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My son and I were working on an Adafruit NeoTrellis M4 Mainboard over the holidays. This amazing little device puts a NeoPixel + an Audio board + a USB port along with a 120 MHz Cortex M4 Core and a mic amplifier and you can program it with CircuitPython. CircuitPython is open source and on Github at https://github.com/adafruit/circuitpython. "CircuitPython is an education friendly open source derivative of MicroPython." It works with a bunch of boards including this NeoTrellis and it's just lovely for teaching and learning.

This item is just the mainboard! You'll almost certainly want two Silicone Elastomer 4x4 Pads and an enclosure to go along.

Circuit PythonAs with a lot of these small boards, when you plug a NeoTrellis into a your machine via USB you'll get new disk drive that pops up. All you have to do to "deploy" your code is copy it to your drive. Even better, why not just edit the code place?

There's a great Python editor called Mu that works well with Circuit Python. However, my son and I are more familiar with Visual Studio Code so we wanted to see how it worked with Circuit Python.

We installed the Python extension for VS Code as well as the Arduino extension for VS Code and the Arduino IDE directly from the Windows Store.

Fire up VS Code and File | Open Folder and open the Disk Drive of the NeoTrellis and open (or create) a code.py file. Then from the Command Palette (Ctrl-Shift-P) in VS Code select Arduino > Initialize. If you get an error you may need to set up the path to your Arduino IDE. If you installed it from the Windows Store like we did you may find it in a weird path. We set the arduino.path like this:

"arduino.path": "C:\\Program Files\\WindowsApps\\ArduinoLLC.ArduinoIDE_1.8.19.0_x86__mdqgnx93n4wtt"

The NeoTrellis M4 also shows up as a COM port so you can look at its Serial Output for debugging purposes as if it were an Arduino (because it is underneath). You then Arduino > Select a COM Port from the Command Palette and it will create a file called .vscode/arduino.json in your folder that will look like this:

{
"port": "COM3"
}

Trellis M4 is awesomeNow, within Visual Studio Code select Arduino > Open Serial Monitor and all of your print("") methods will output to that bottom pane.

Of course, we could putty into the COM Port but since I'm using this as a learning tool with my 11 year old, I find that a single window that shows both the console and the code help them focus, rather than managing multiple windows.

At this point we have a nice Developer Inner Loop going. That inner loop for us (the developers) is that we can write some code, hit save (Ctrl-S) and get immediate feedback. The application restarts when it detects the code.py file has changed and any debug (print) statements appear in the console immediately.

Visual Studio Code doing some Circuit Python

We are really enjoying this Adafruit NeoTrellis M4 Express kit. Next we're going to make a beat sequencer since the Christmas Soundboard was such a hit with mom!


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How to set up ASP.NET Core 2.2 Health Checks with BeatPulse's AspNetCore.Diagnostics.HealthChecks

December 12, '18 Comments [5] Posted in ASP.NET | DotNetCore | Open Source
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Availability TestsASP.NET Core 2.2 is out and released and upgrading my podcast site was very easy. Once I had it updated I wanted to take advantage of some of the new features.

For example, I have used a number of "health check" services like elmah.io, pingdom.com, or Azure's Availability Tests. I have tests that ping my website from all over the world and alert me if the site is down or unavailable.

I've wanted to make my Health Endpoint Monitoring more formal. You likely have a service that does an occasional GET request to a page and looks at the HTML, or maybe just looks for an HTTP 200 Response. For the longest time most site availability tests are just basic pings. Recently folks have been formalizing their health checks.

You can make these tests more robust by actually having the health check endpoint check deeper and then return something meaningful. That could be as simple as "Healthy" or "Unhealthy" or it could be a whole JSON payload that tells you what's working and what's not. It's up to you!

image

Is your database up? Maybe it's up but in read-only mode? Are your dependent services up? If one is down, can you recover? For example, I use some 3rd party back-end services that might be down. If one is down I could used cached data but my site is less than "Healthy," and I'd like to know. Is my disk full? Is my CPU hot? You get the idea.

You also need to distinguish between a "liveness" test and a "readiness" test. Liveness failures mean the site is down, dead, and needs fixing. Readiness tests mean it's there but perhaps isn't ready to serve traffic. Waking up, or busy, for example.

If you just want your app to report it's liveness, just use the most basic ASP.NET Core 2.2 health check in your Startup.cs. It'll take you minutes to setup.

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
services.AddHealthChecks(); // Registers health check services
}

public void Configure(IApplicationBuilder app)
{
app.UseHealthChecks("/healthcheck");
}

Now you can add a content check in your Azure or Pingdom, or tell Docker or Kubenetes if you're alive or not. Docker has a HEALTHCHECK directive for example:

# Dockerfile
...
HEALTHCHECK CMD curl --fail http://localhost:5000/healthcheck || exit

If you're using Kubernetes you could hook up the Healthcheck to a K8s "readinessProbe" to help it make decisions about your app at scale.

Now, since determining "health" is up to you, you can go as deep as you'd like! The BeatPulse open source project has integrated with the ASP.NET Core Health Check API and set up a repository at https://github.com/Xabaril/AspNetCore.Diagnostics.HealthChecks that you should absolutely check out!

Using these add on methods you can check the health of everything - SQL Server, PostgreSQL, Redis, ElasticSearch, any URI, and on and on. Just add the package you need and then add the extension you want.

You don't usually want your health checks to be heavy but as I said, you could take the results of the "HealthReport" list and dump it out as JSON. If this is too much code going on (anonymous types, all on one line, etc) then just break it up. Hat tip to Dejan.

app.UseHealthChecks("/hc",
new HealthCheckOptions {
ResponseWriter = async (context, report) =>
{
var result = JsonConvert.SerializeObject(
new {
status = report.Status.ToString(),
errors = report.Entries.Select(e => new { key = e.Key, value = Enum.GetName(typeof(HealthStatus), e.Value.Status) })
});
context.Response.ContentType = MediaTypeNames.Application.Json;
await context.Response.WriteAsync(result);
}
});

At this point my endpoint doesn't just say "Healthy," it looks like this nice JSON response.

{
status: "Healthy",
errors: [ ]
}

I could add a Url check for my back end API. If it's down (or in this case, unauthorized) I'll get this a nice explanation. I can decide if this means my site is unhealthy or degraded.  I'm also pushing the results into Application Insights which I can then query on and make charts against.

services.AddHealthChecks()
.AddApplicationInsightsPublisher()
.AddUrlGroup(new Uri("https://api.simplecast.com/v1/podcasts.json"),"Simplecast API",HealthStatus.Degraded)
.AddUrlGroup(new Uri("https://rss.simplecast.com/podcasts/4669/rss"), "Simplecast RSS", HealthStatus.Degraded);

Here is the response, cool, eh?

{
status: "Degraded",
errors: [
{
key: "Simplecast API",
value: "Degraded"
},
{
key: "Simplecast RSS",
value: "Healthy"
}
]
}

This JSON is custom, but perhaps I could use the a built in writer for a free reasonable default and then hook up a free default UI?

app.UseHealthChecks("/hc", new HealthCheckOptions()
{
Predicate = _ => true,
ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
});

app.UseHealthChecksUI(setup => { setup.ApiPath = "/hc"; setup.UiPath = "/healthcheckui";);

Then I can hit /healthcheckui and it'll call the API endpoint and I get a nice little bootstrappy client-side front end for my health check. A mini dashboard if you will. I'll be using Application Insights and the API endpoint but it's nice to know this is also an option!

If I had a database I could check one or more of those for health well. The possibilities are endless and up to you.

public void ConfigureServices(IServiceCollection services)
{
services.AddHealthChecks()
.AddSqlServer(
connectionString: Configuration["Data:ConnectionStrings:Sql"],
healthQuery: "SELECT 1;",
name: "sql",
failureStatus: HealthStatus.Degraded,
tags: new string[] { "db", "sql", "sqlserver" });
}

It's super flexible. You can even set up ASP.NET Core Health Checks to have a webhook that sends a Slack or Teams message that lets the team know the health of the site.

Check it out. It'll take less than an hour or so to set up the basics of ASP.NET Core 2.2 Health Checks.


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.